A pressure sensor in which even if a pressure medium is brought into direct contact with the pressure receiving plane of a pressure detection element or with a bonding wire connected to the pressure receiving plane, the pressure detection element is protected and an electric leak is prevented is proposed in the related art, for example, in a patent document 1.
Specifically, the patent document 1 proposes the pressure sensor including: a housing into which a pressure medium is introduced; a case mounted in the housing; a sensor chip as a pressure detection element which is mounted in the case and has a pressure receiving plane on which pressure from the pressure medium is received; a terminal mounted around the sensor chip of the case; and a bonding wire whose one end is electrically connected to the pressure receiving plane of the sensor chip and whose other end is electrically connected to the terminal.
In this pressure sensor, a middle portion between the one end and the other end of the boding wire is coated with a first coating material having electric insulation and resistance to the pressure medium. Moreover, the connection portion of the bonding wire and the sensor chip, the connection portion of the bonding wire and the terminal, and the pressure receiving plane of the sensor chip are coated with a second coating material having electric insulation and resistance to the pressure medium.
The sensor chip is mounted in the case in such a way that the pressure receiving plane is vertical to the direction in which the pressure medium is introduced. The bonding wire is extended in a direction vertical to the direction, in which the pressure medium is introduced, from the pressure receiving plane of the sensor chip and is connected to a terminal arranged on the same plane as the pressure receiving plane. Moreover, the housing and the case are sealed from each other via an O ring of a sealing part arranged so as to surround the sensor chip, the bonding wire, and the terminal.
The above-mentioned pressure sensor is constructed in such a way that the pressure medium is directly introduced to the pressure receiving plane of the sensor chip, but the bonding wire and the pressure receiving plane of the sensor chip are coated with the coating material. Hence, the sensor chip can be protected and an electric leak can be prevented.    [Patent Document] JP-2006-208088A
However, in the related art, the pressure receiving plane of the sensor chip is arranged vertically to the direction in which the pressure medium is introduced and hence the bonding wire needs to be extended on the same plane as the pressure receiving plane from the pressure receiving plane of the sensor chip, which results in enlarging the outside diameter of the case. In this case, the outside diameter needs to be increased in consideration of the arrangement of the O ring surrounding the terminal and the like. In this manner, the related art presents a problem that the outside diameter of the pressure sensor results in being enlarged.
Moreover, the first coating material with which the bonding wire is coated performs the function of protecting the boding wire from the pressure medium but the pressure of the pressure medium is directly applied to the bonding wire. That is, there is presented a problem that the bonding wire is broken by the pulsation of the pressure medium, which results in interrupting the electric connection of the sensor chip and the terminal.
Thus, it is required to reduce the size of a pressure sensor and to prevent the electric connection of a sensor chip and a terminal from being interrupted.
Further, a pressure sensor having its size reduced is proposed in the related art, for example, in a patent document 2. Specifically, the patent document 2 proposes a structure in which a resin case has a wiring board mounted on its one end portion and in which a sensor chip formed of a semiconductor substrate is flip-chip bonded to the one plane of the wiring board via bumps.
The wiring board is electrically connected to terminals inserted and molded in the case and is mounted on the case with the plane of the board directed in parallel to the radial direction of the pressure sensor. Moreover, a gage part for detecting pressure is formed in the central portion of a square pressure receiving plane of the sensor chip and the bumps are disposed on four corners of the pressure receiving plane. The sensor chip is flip-chip bonded to the wiring board via the bumps, whereby the sensor chip, the wiring board, the terminals are electrically connected to each other. With this, the sensor chip is disposed in parallel to the wiring board and hence the pressure receiving plane of the sensor chip is directed in parallel to the radial direction of the pressure sensor.
In this manner, the electric connection portions of the sensor chip are connected not by wire bonding but by flip-chip bonding requiring a smaller area, so that the size of the pressure sensor can be reduced.    [Patent Document 2] JP-2006-177925A Corresponding to U.S. Pat. No. 7,210,357
However, the related art described above presents the following problem: that is, when the pressure sensor receives ambient temperature and the temperature of a pressure medium, because the case made of resin, the bump made of metal, and the sensor chip made of semiconductor are different from each other in the coefficient of linear expansion, a thermal stress is caused by the expansion of the case made of resin having the largest coefficient of linear expansion and is transmitted to the sensor chip made of semiconductor having the smallest coefficient of linear expansion via the wiring board and the bumps.
As described above, since the bumps are disposed on the four corners of the pressure receiving plane, the thermal stress is directly transmitted to the gage part via paths in four directions. In other words, the gage part is distorted by the thermal stress in four directions. Thus, pressure including pressure produced by the distortion caused by the thermal stress is detected in the gage part. This reduces the accuracy of detecting the pressure.
Thus, it is required to provide a pressure sensor that can make it harder for thermal stress to be transmitted to a gage part and a method for manufacturing the pressure sensor.